Polyethylene terephthalate (PET) is most commonly used as a base material of conductive films, and this is followed by such materials as polyethylene sulfonate (PES), polycarbonate (PC) or polyarylate (PAR), which are used less frequently than PET. In addition, although examples of conductive substances include inorganic materials such as indium tin oxide (ITO), tin oxide (SnO), zinc oxide (ZnO) or cadmium tin oxide (CdSnO4), ITO is used most commonly from the viewpoints of high conductivity and visible light transmission. Under the present circumstances, ITO-PET conductive films are applied in the form of flexible devices to various electronic devices. However, since PET uses fossil fuels in the manufacturing process thereof, it has a considerable effect on the environment with respect to reducing levels of fossil fuels, global warming and the like. In addition, since there are limitations on indium reserves, there is the risk of these reserves being depleted in the near future if indium continues to be used in this manner, and due to its price becoming extremely high, there is a pressing need to find an alternative among other materials.
On the other hand, growing attention is being focused on polysaccharides derived from natural materials for use as environmentally-friendly materials. Cellulose is contained in such sources as plant cell walls and external secretions of microorganisms or the mantle of sea squirts, is the most commonly found type of polysaccharide in the world, and is expected to be applied and deployed in carious fields due to its biodegradability, high crystallinity and superior stability and safety.
Since cellulose contains strong hydrogen bonds within its molecules and has high crystallinity, making it practically insoluble in water and ordinary solvents, considerable research has been conducted to improve its solubility. In particular, a technique that introduces a carboxyl group via an aldehyde by oxidizing the primary hydroxyl group at position C6 using a TEMPO (2,2,6,6-tetramethylpiperidinooxy radical) catalyst system makes possible to selectively oxidize only the primary hydroxyl group, and this technique has attracted attention in recent years since the reaction can also be carried out under mild conditions (aqueous system, room temperature). When TEMPO oxidation is carried out using natural cellulose, only the surface can be oxidized on the nanometer level while maintaining the crystallinity of cellulose. After washing, fine, modified cellulose can be uniformity dispersed in water by simply adding slight mechanical treatment.
An aqueous cellulose dispersion prepared using this method has a particle width on the nanometer order and is homogeneous, and as a result of drying, demonstrates high transparency in the visible light range and allows the obtaining of a film having high strength, thereby resulting in expectations for its application and deployment in various fields.
An example of a conductive base material using cellulose is described in Patent Document 1, which describes a conductive polymer composite paper produced by incorporating a conductive polymer in paper pulp. In addition, Patent Document 2 describes conductive paper obtained by mixing cellulose with a conductive substance.